It is well known to provide slide projectors of the type having a tray receiving groove adapted to alternately receive slide trays of different configurations, and having means for indexing any such slide trays disposed in the groove from one slide position to the next, so that all of the slides in such tray may be sequentially advanced to the viewing position. In most instances, the alternate tray configurations consist of a horizontally disposed box type rectangular tray and a vertically disposed circular tray, the object being to increase the slide holding capacity by the use of the circular tray. Both such tray configurations are provided with a peripheral rack of teeth or other projections, each of which corresponds to a slide receiving space therein, and an indexing gear in the projector is adapted to operatively engage such teeth or projections on either tray to sequentially advance such tray from slide to slide. An example of a projector of this type is shown in U.S. Reissue Pat. No. Re 26,619 to Hall.
The Hall device, which is typical of projectors of this type, includes a single indexing drive gear adapted to engage the teeth of either a box tray or a circular tray. For support and guidance purposes the box type tray rests on the bottom surface of the tray receiving groove, and is held thereby in engagement with the indexing gear. In addition, a pair of spaced support lugs are provided on a side wall of the slide tray receiving groove to engage two points along the outer periphery of the circular tray, and a projection or guide surface formed on the opposite wall of the tray receiving groove holds the tray in contact with such projections. In this manner, the circular tray is properly positioned for engagement with the indexing gear. In some instances the lowermost point of the circular tray is also adapted to rest upon the bottom surface of the tray receiving groove for additional support. It should be noted that on most projectors of this type the pitch of the indexing racks formed on both the box tray and the circular tray are identical, so that the same incremental rotation of the indexing gear is adapted to advance either of said trays the appropriate distance.
Unfortunately, although the foregoing described projectors are in widespread use, they are generally acceptable for use only with slide trays manufactured specifically for a particular projector, and are incapable of use with alternate slide trays having different support and indexing configurations. Accordingly, if an individual has one or more slide trays produced by one manufacturer, such trays generally cannot be utilized in a slide projector produced by another manufacturer. In addition, in some instances circular trays and box type trays produced by the same manufacturer cannot be utilized in a single projector produced by the same manufacturer because each of such trays has different support and indexing requirements. To overcome this deficiency, some manufacturers have provided removable adaptors to be positioned within the tray receiving groove for supporting either the box tray or the circular tray. Such adaptors may also include a reduction gear network which provides a drive linkage between a main indexing gear, which is adapted to normally engage one of said trays, and the indexing rack of the alternate tray, so that each of said trays is advanced the appropriate distance from slide to slide.
An example of a removable adaptor for the purpose of accommodating a circular tray in a projector normally adapted for use with a box tray is disclosed in U.S. Pat. No. 3,572,921 to Mulch. The Mulch adaptor permits the alternate use of box trays and circular trays of different configurations within the same slide projector. However, the adaptor is quite inconvenient to use, costly to construct, and can in many instances cause jamming of one of the two slide trays if it is not properly installed. Furthermore, the Mulch device comtemplates the use of a box tray and circular tray produced by the same manufacturer for use in a specified projector also produced by the same manufacturer.